In the Aug. 10 issue, we wrote about the centennial of condenser microphones. Let’s look more closely at electret condenser microphones. Fig. 1: The few components that make up an electret microphone.

Fig. 1: Diagrams from Wente’s 1916 patent application show the condenser microphone in cutaway view. Diaphragm (#6), which is grounded, is stretched only 5/10000th of an inch from the backplate (#7), ...